Camouflage material

ABSTRACT

The invention regards a material having a three-dimensional surface built up by bulgings arranged regularly or irregularly mutually adjacently, and which have approximately conical form. It is thus accomplished that the brightness of the material is little dependent on the view angle, in contrast to what is the case with plane surfaces, even if painted with matte camouflage paint.

The invention regards a camouflage material having a three-dimensionalsurface structure, consisting of mutually adjacent bulgements that arepointed.

Three-dimensional surface structures for camouflage purposes arepreviously known. An example is U.S. Pat. No. 3,069,796, whichdemonstrates camouflage layers which are cut in a particular way suchthat when stretched they assume a foliage-like structure. Anotherexample is U.S. Pat. No. 3,836,967, which shows a radar camouflagehaving a multitude of similar hollow tapered pyramid-formed projectionswhich are packed to each other and form a kind of a conducting layer.

A particular problem when camouflaging illuminated objects (includingreconnaissance means in both visible and invisible light) is thedifficulty of obtaining something, which resembles nature in all. Aparticular difficulty is that prior art camouflage surfaces appear sodifferently in different angles of regarding and illuminationrespectively. Thus, a grass surface has about the same colour and not sobig difference in brightness seen against the light in comparison tolight falling in at 90° or seen in the light direction. For instance, apainted tin plate will show itself very bright seen against the light,and this independent of how good and matte a camouflage paint is used tocover the tin plate.

It is for instance shown in practice that a construction such as thatshown in U.S. Pat. No. 3,836,967 is rather inappropriate for thedisguise or camouflage purpose of the present invention, since itsthree-dimensional structure is composed from plane surfaces, which givea specular reflection, which is without importance for the use envisagedtherewith, which is for radar camouflage. In visible light and e.g. thenear infrared, the aspect will be far from natural.

The problem of the invention is solved according to the presentinvention by obtaining a three-dimensional surface that in everydirection has a minimum of plane, specularly reflective surfaces. Morespecifically, the invention regards a camouflage material having athree-dimensional surface structure consisting of mutually adjacentpointed bulgings, characterized in having curved surfaces in essentiallyall sight directions.

The bulgings being stated as pointed is to be understood such that somesection through them will form a sectional curve that at the top isessentially angular but can be somewhat rounded. Endings as more or lesspronounced apices or edges are however preferred. If they are made aspointed, the point itself in practice will be somewhat rounded, which isalso true for an edge form.

According to a preferred embodiment, the bulgings are essentiallyconical bulgings. With cones are to be understood according to theinvention such forms which can be described by a point, a closeddirectrix curve which may be arbitrary or a polygon made of straight orcurved lines, a circle, an ellipse, etc. and a generatrix. In the mostcommon cases, a generatrix is a straight line, but according to the moregeneral definition intended here, it is possible for a generatrix to beused also a curved line.

The essential is that the bulging will show up in practically alldirections as curved surfaces. Simply curved surfaces will then give aspecular reflection along a line. Doubly curved surfaces will give aspecular reflection only in a point.

In a preferred embodiment, bulgings are used having a directrix which iscircular or near circular. It is also preferred to use essentiallystraight lines as generatrices. According to a preferred embodiment,they will also have such angles of clearance that they easily releasefrom a mold when made by molding.

In addition to the visual effect, it is also possible to obtain a radarcamouflage effect, for example by arranging under the three-dimensionalstructure of a layer having radar absorption properties, which isaccomplished by arranging the surface resistance as known from U.S. Pat.No. 3,733,606. Also colouring or the like with different kinds of priorart camouflage dyes is possible, as arranging favourable properties inother radiation wavelength intervals.

The invention shall now be described by example and appertainingfigures.

FIG. 1 shows an example of a camouflage material according to theinvention.

FIG. 2 shows a comparison of brightness for different angles of view ofa camouflage painted tin plate, a natural grass surface and a camouflagematerial built up from cones.

FIGS. 3A and 3B and FIGS. 4A and 4B respectively show colour recordingsfor a camouflage painted tin plate and a surface according to theinvention respectively.

In FIG. 1 is shown a non-limiting example of a camouflage material ofthe kind designated by the invention. On a surface are moulded plasticcones having a height of 5 mm and about 60° cone angle and in displacedrows having a mutual distance of 5 mm. In this case, the symmetry ishexagonal, there being six nearest neighbours to each cone.Alternatively, they may be ordered in quincunx position, i.e. with fournearest neighbours to each cone.

The cone-formed bulgings can also be in a more random disorder, even ifan ordered structure is preferred, not least for reasons of manufacture.Further, the sizes of the cones may vary within relatively large limits,as from the height of 1 mm to 50 mm. The height of 5 mm is a suitablebalance value in view of tolerance of dirt, which is diminished withsmall cones, and material consumption and weight, which increase withlarger cones.

FIG. 2 shows a diagram where luminance has been measured as a functionof the view angle, measured between grazing incidence and against thelight (−90°) and grazing incidence and along the light (+90°), for threedifferent surfaces: The curve 1 designates a tin plate surface paintedwith a matte camouflage paint, curve 2 a natural grass surface and curve3 a surface such as shown in FIG. 1. The luminance is reproduced inarbitrary but linear units. The measurements were made in sunlight on agrass lawn, with for curve 1 a painted tin plate laid upon the ground,and for the curve 3 a plate with cones according to the invention, laidin the same way upon the ground.

It is seen from the figures that the painted tinplate is particularlyunfavourable in counter light. Hardly any object in nature, exceptingpossibly water surfaces, show such brightness in counter light. In viewof the fact that just tin plate surfaces and the like are the mostcommon of that military material which needs camouflaging, it is clearthat an improvement in this respect is of great importance.

The grass surface, corresponding to curve 2, must be considered as thatwhich is most desirable to attain. Relative to this, the exemplaryconstruction as of curve 3 is a satisfactory imitation.

The exemplary construction used is made from opaque material. Theincrease in luminance observed in the forward light direction isdependent thereof; a grass surface consists of leaves that have acertain transparency. If the cone material is made somewhat transparent,the result will be more natural. In a preferred embodiment therefore,the cones are made of some transparent material, and preferentiallyhollow.

FIGS. 3A, 3B show colour diagrams regarding painted tin plate measuredat different sight angles. FIG. 3A thus shows in a diagram according toCIE 1931 that the camouflage painted plate changes colour when changingthe angle of sight between grazing counter light and grazing forwardlight. FIG. 3B shows with the same x-axis as in FIG. 3A the luminosity(scale arbitrary but linear) when the angle is changed from grazingforward light (leftmost) to counter light (rightmost in the diagram). Asa comparison, FIGS. 3A and 3B show similar measurements for a surfacehaving cones according to the invention. The inventive surface thus hasconsiderably better properties both as to brightness and colour forvarying sight angles. All those diagrams were recorded by means of aMinolta Chromameter, mod. CS 100.

From those diagrams thus appears that there are also rather greatchanges in colour when the angle of sight is changed. FIG. 3B and FIG.4B corroborate the result shown in FIG. 2.

The intended three-dimensional structure can be manufactured in manyways, as will be understood by the man of the art knowledgeable inplastics. One way is by moulding, another by embossing of a sheet,preferentially afterwards mounted upon a carrier sheet which can bewoven or a plastic sheet. It is also possible to make this structurefrom metal.

Although the invention has been exemplified with a structure havingcertain dimensions, it is clear that those may be varied in differentways, depending upon the purpose. The inventive effect is obtained alsowith the same structure in greater or smaller scale. Great scale andmassive embodiment will lead to great material consumption and a patternvisible at near distance. At small scale, there may be difficulties ofmanufacture, as well as difficulties in cleaning.

Depending on the circumstances, the surface may be dyed with differentcamouflage dyes/paints, such as summer colours, winter colours or desertcolours. Those dyes/paints should have camouflage properties within alarge wavelength interval, from UV up to and within the near infraredinterval. The material may be made self-supporting or be affixed to e.g.vehicles or tanks.

Further, this material may be used for partly covering surfaces, or bemade less regular than as has been exemplified.

What is claimed is:
 1. Camouflage material having an optical camouflageeffect, having a three-dimensional surface structure consisting ofmutually adjacent bulgings, characterized in that said bulgings arepointed and have curved surfaces in essentially all sight directions. 2.Camouflage material according to claim 1, characterized in that the saidbulgings are essentially circularly conical bulgings.
 3. Camouflagematerial according to claim 2, characterized in that said circularlyconical bulgings have straight-line generatrices.
 4. Camouflage materialaccording to claim 2, characterized in that said bulgings havegeneratrices that are curved lines.
 5. Camouflage material according toclaim 1, characterized in that the bulgings are cones having directricesthat are polygons of straight lines and generatrices that are curved. 6.Camouflage material according to any one of the preceding claims,characterized in that the bulgings are regularly ordered quincuncially,having four nearest neighbours to each bulging.
 7. Camouflage materialaccording to any one of claims 1-5, characterized in that the bulgingsare regularly ordered in a hexagon pattern, having six neighbours toeach bulging.
 8. Camouflage material according to claim 1 characterizedin that its bulgings are at least partially transparent.
 9. Camouflagematerial according to claim 1 characterized in that it is made from aplastic or elastomer material.
 10. Camouflage material according toclaim 1 characterized in that it contains electrically conductingmaterial and/or magnetic material.
 11. Camouflage material according toclaim 10, characterized in that the electrically conducting material isarranged in a carrier structure which is arranged on the under side andcarries the bulgings.